The proposed research is intended to elucidate a variety of problems within the broad field of thyroidology. The over-all intent is to clarify multiple aspects of thyroid hormone economy in normal animals and human and in patients with thyroid disfunction. Among the major topic categories to be studied are: 1. Studies of the Hypothalamic- Pituitary Regulation of TSH. 2. The Intermediary Metabolism of Thyroid and its Relation to Hormonal Synthesis and Function. 3. The Response of the Normal and Abnormal Thyroid to Acute and Chronic Variations in the Availability of Iodide. 4. Studies of Thyroid Hormone Transport and Metabolism. 5. Studies of the Specific Metabolites of Peripheral Thyroxine Metabolism and their Physiological Role. 6. Studies Related to the Pathogenesis, Physiopathology, and Natural History of Thyroid Disorders. Within each of these broad categories, several individual studies are proposed.